Curtis 


TESTING- 


THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

LOS  ANGELES 

GIFT  OB 

Dean  L.  i;U  K.  Eoelter 


DEPARTMENT   OF   COMMERCE 


CIRCULAR 

OF  THE 

BUREAU  OF  STANDARDS 

S.  W.  STRATTON.  DIRECTOR 

No.  107 
THE  TESTING  QF_  PAPER  ^ 


FEBRUARY  12,  1921 


PRICE,  10  CENTS 

Sold  only  by  the  Superintendent  of  Documents,  Government  Printing  Office 
Washington,  D.  C. 

WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 
1921 


DEPARTMENT    OF   COMMERCE 


CIRCULAR 

OF  THE 

BUREAU  OF  STANDARDS 

S.  W.  STRATTON,   DIRECTOR 


No.  1O7 
THE  TESTING  OF  PAPER 


FEBRUARY  12,  1921 


PRICE,  10  CENTS 

Sold  only  by  the  Superintendent  of  Documents,  Government  Printing  Office 
Washington,  D.  C. 

WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 
-  1921 


THE  TESTING  OF  PAPER 


ABSTRACT 

This  circular  contains  information  relating  to  the  methods  of  testing  and  the  appa- 
ratus employed  in  the  paper  laboratories  of  the  Bureau  of  Standards  for  the  routine 
testing  of  paper.  In  the  introduction  a  brief  description  of  the  raw  materials  used, 
the  size  and  importance  of  the  paper  industry,  and  the  general  groups  or  classes  of 
paper  are  given.  The  classification  of  paper  is  only  of  a  general  nature.  The  pur- 
pose of  such  tests  and  the  development  of  methods  of  testing  is  touched  upon,  and 
suggestions  are  given  as  to  the  methods  of  developing  specifications. 

The  testing  of  paper  is  divided  into  three  groups,  and  the  methods  are  classed  as 
physical,  chemical,  and  microscopical.  Under  each  group,  the  various  standard 
methods  are  given  in  detail  with  photographs  of  apparatus  employed.  No  attempt 
is  made  in  this  circular  to  interpret  results  of  tests.  It  is  brought  out  that  changes  of 
temperature  and  humidity  affect  the  physical  qualities  of  paper,  and  for  this  reason  a 
constant-temperature  and  humidity  room  has  been  installed .  It  has  not  been  possible 
to  give  the  relation  between  humidity  and  temperature  changes  and  the  physical 
characteristics  of  paper,  but  it  is  hoped  to  have  this  information  available  later.  The 
chemical  testing  of  paper  is  concerned  with  the  determination  of  the  amount  and  kind 
of  filler  or  loading  materials  used  and  the  amount  and  kind  of  sizing  in  the  paper, 
and  the  methods  are  given  in  some  detail,  both  qualitative  and  quantitative.  It 
is  desirable  to  know  the  kinds  of  fibrous  materials  out  of  which  a  sheet  of  paper  is  made 
and  for  this  purpose  certain  stains  are  used  to  color  the  fibers  on  a  microscopical  slide. 
The  procedure  is  given,  and  suggestions  are  made  as  to  the  value  of  microphotographs. 
A  short  working  bibliography  is  included,  as  well  as  regulations  for  tests  and  methods 
of  sampling  and  submission  of  samples  for  test. 


CONTENTS  Page 

I.  Introduction •        4 

1 .  Size  of  industry 5 

2 .  Raw  materials 5 

3 .  Definition  and  types  of  paper 6 

II.  Quality  of  paper 7 

1 .  Purpose  of  tests 7 

2.  Development  of  test  methods 7 

3.  Specifications 8 

(a)  Formulation 9 

(6)  Nomenclature 9 

(c)  Quality  standards 9 

(d)  Technical  practice 9 

III.  Physical  testing 10 

1 .  Weight 10 

2 .  Thickness 13 

3 .  Bursting  strength 14 

4.  Tensile  strength 15 

5 .  Folding  endurance 17 

6.  Tearing  strength 18 

7 .  Absorption 20 

8.  Transparency 22 


4  Circular  of  the  Bureau  of  Standards 

Page 
IV.  Chemical  testing 23 

1 .  Loading  material 23 

2.  Sizing 25 

(a)  Total  resins 25 

(b)  Starch 27 

(c)  Glue 27 

V.  Microscopical  testing 28 

1 .  Procedure 28 

2 .  Estimation 31 

3 .  Microphotography 32 

VI.  Bibliography 32 

1 .  Books 32 

2.  Periodicals 32 

3 .  Government  publications 35 

VII.   Regulations  regarding  tests 35 

1.  Fees 35 

2.  Sampling. .  .  37 

I.  INTRODUCTION1 

The  testing  of  paper  by  means  of  scientific  methods  has  received 
an  increasing  amount  of  attention  in  the  United  States  during  the 
past  10  years.  This  has  been  brought  about  largely  by  the  increase 
in  the  number  of  technically  trained  men  in  the  industry  and  the 
desire  of  placing  empirical  and  practical  tests  upon  a  more  accurate 
basis. 

The  purpose  of  this  circular  is  to  describe  the  methods  of  testing 
paper  as  used  by  the  paper  section  ot  the  Bureau  of  Standards  and 
adopted  as  a  result  of  testing  a  large  number  of  samples  of  various 
kinds  of  paper  during  a  period  of  years.  These  methods  are  those 
that  are  in  common  use  in  paper-testing  laboratories  and  are  given 
to  fill  a  need  expressed  by  laboratories  and  the  general  public. 
Proposed  new  methods  and  special  tests  are  not  included  in  this 
circular,  but  these  will  be  published  separately  as  they  are 
developed. 

The  structure  of  paper  is  such  that  there  is  variation  in  some  ot 
its  characteristics,  even  in  a  single  sheet.  It  is  therefore  obvious 
that  precaution  must  be  taken  to  sample  a  lot  of  paper  in  such  a 
way  as  to  obtain  a  test  sample  representative  of  the  whole  lot. 
It  is  also  necessary  to  make  a  sufficient  number  of  tests  in  each  case, 
in  order  that  an  average  result  may  be  obtained.  It  is  important 
to  obtain  this  average  by  testing  10  sheets  of  paper,  rather  than  by 
making  10  tests  on  a  single  sheet. 

1  This  circular  was  prepared  by  F.  A.  Curtis,  chief,  paper  section,  Bureau  of  Standards,  and  contains 
information  relating  to  the  methods  of  testing  and  the  apparatus  employed  in  the  paper  laboratories  of  this 
Bureau  for  the  routine  testing  of  paper. 


The  Testing  of  Paper  5 

1.  SIZE  OF  INDUSTRY 

The  production  of  paper  in  the  United  States  has  increased  ap- 
proximately 55  per  cent  in  the  last  10  years,  and  there  is  now  being 
manufactured  annually,  in  the  United  States,  approximately 
7,000,000  tons  of  paper  of  all  kinds.  The  pulp  and  paper  industry 
in  1914  ranked  sixth  among  the  industries  of  the  United  States  in 
regard  to  the  amount  of  capital  invested  and  in  regard  to  the  value 
of  the  product,  and  ranked  fourth  in  regard  to  the  value  added  by 
manufacture.  It  can  thus  be  readily  seen  that  the  pulp  and  paper 
industry  is  an  important  one,  and  there  is  little  doubt  but  that  tech- 
nical development  is  essential  for  the  future  of  the  industry. 

2.  RAW  MATERIALS 

Paper  can  be  made  from  most  fibrous  vegetable  matter,  but 
technical  difficulties,  cost  of  manufacture,  and  grade  of  paper 
produced  preclude  the  use  of  many  fibrous  materials.  Wood 
pulp,  old  rags,  old  papers,  straw,  and  old  rope  are  the  substances 
generally  in  use  in  this  country.  Wood  pulp  is  produced  by  four 
processes,  one  of  which,  "ground  wood"  pulp,  is  mechanical, 
while  the  other  three,  "sulphite,"  "soda,"  and  "sulphate,"  are 
largely  chemical.  There  are  a  large  number  of  commercial  grades 
of  rags  and  waste  paper.  All  these  materials  are  used  in  different 
classes  of  paper  for  different  purposes,  or  in  many  cases  mixtures 
are  made  to  produce  certain  qualities  in  paper.  In  addition  to 
the  fibrous  material  entering  into  the  manufacture  of  paper, 
certain  noncellulose  materials  are  necessary  or  desirable.  The 
addition  of  rosin  sizing  to  paper  pulp,  and  its  precipitation  by 
alum,  gives  the  finished  paper  certain  difficultly  definable  qualities. 
Clays  and  similar  materials,  when  added,  produce  a  more  even  or 
smooth  surface  to  the  paper  which  is  necessary  for  some  kinds  of 
printing. 

Experiments  have  been  made,  some  of  them  a  hundred  years 
ago,  to  produce  paper  from  various  kinds  of  grasses  and  fibrous 
material.  An  incomplete  list  is  here  given:  Asparagus,  bagging, 
bamboo,  banana,  beet  root,  blue  grass,  bran,  broom  corn,  cabbage 
stumps,  coconut  husks,  cottonseed  hulls,  cotton  stalks,  corn 
husks,  palm,  esparto,  ferns,  flax,  grapevines,  hay,  hemp,  leaves, 
moss,  mulberry,  nettles,  peat,  plantain,  reeds,  rice  straw,  rushes, 
sawdust,  seaweed,  thistles,  tow,  and  many  others.  Some  of 
these  experiments  have  been  successful  on  a  laboratory  scale, 
some  have  even  produced  paper  in  large  enough  quantity  for 
printing,  but  only  a  few  have  ever  reached  a  commercial  standing. 

A  study  of  Table  i  brings  out  an  interesting  change  in  the 
proportions  of  various  raw  materials  used  at  various  periods. 


Circular  of  the  Bureau  of  Standards 


TABLE  1. — Percentage  Proportions  of  Constituent  Materials  Used  in  Paper  Making, 
by  Decades,  Since  1880 


Materials 

1880 

1900 

1910 

1918 

Rags  

Per  cent 
30 

Per  cent 
14 

Per  cent 
8 

Per  cent 
6 

Straw 

40 

21  5 

6  5 

5  5 

Wood  pulp  

14 

38 
21 

61 
21 

57 
30 

Miscellaneous  

16 

5.5 

3.5 

1.5 

It  is  to  be  noted,  however,  that  wood  pulp  was  used  to  some 
extent  in  1 880,  but  was  not  recorded  and  tabulated  as  a  separate 
item. 

3.     DEFINITION  AND  TYPES  OF  PAPER 

Paper  is  a  matted  or  felted  structure  of  fibrous  material,  formed 
into  a  relatively  thin  sheet.  It  is  composed  essentially  of  cellulose 
fibers  obtained  from  vegetable  growths  in  a  more  or  less  pure  state. 
These  fibers  may  be  grouped  as. follows:  (a)  Seed  fibers,  or  seed 
hairs,  (6)  stem  or  bast  fibers,  (c)  leaf  fibers,  (d)  fruit  fibers,  and  (e) 
wood  fibers.  In  general,  it  is  customary  to  consider  and  classify 
paper  according  to  its  use  rather  than  according  to  its  constituents. 
In  the  testing  of  paper  the  use  to  which  it  is  to  be  put  determines 
the  kinds  of  tests  necessary  to  evaluate  its  quality. 

The  classification  of  the  various  types  of  paper  has  not  reached  a 
satisfactory  state,  and  the  nomenclature  and  trade  names  are 
often  very  confusing  to  the  layman.  This  is  largely  due  to  the 
lack  of  standardization,  the  difficulty  of  defining  numerically 
certain  qualities,  and  the  fact  that  the  distinctive  line  between 
various  kinds  of  paper  is,  in  many  cases,  so  slight  that  it  is  almost 
impossible  to  tell  by  what  name  to  call  it.  The  following  general 
classes  of  paper  given  in  Table  2  refer  to  broad  types,  and  in 
each  class  there  are  variations  of  constituents  as  well  as  quality: 

TABLE  2.— Percentage   Output  of  the  Several  Classes  of  Paper  Products 


Paper  products 

Percentage 
of  total, 
1918 

Fibrous  materials  used  in  varying  proportions 

Boards  
Building  
Blotting 

30.4 
5.3 
2 

Old  paper,  wood  pulp,  straw,  old  rope 
Old  paper,  wood  pulp,  asbestos,  waste,  rages,  etc. 

Book  and  cover  
News  and  hanging  
Tissue  

15.3 
23.3 
2.0 

Rags,  chemical  wood  pulp 
Mechanical  and  chemical  wood  pulp 
Chemical  wood  pulp,  rags,  old  rope 

Wrapping  
Fine  (writing,  bonds,  etc.)  
Specialties  

16.8 
5.8 
.9 

Old  rope,  rags,  sulphite,  and  sulphate  wood  pulp 
Rags  and  chemical  wood  pulp 

The  Testing  of  Paper  7 

II.  QUALITY  OF  PAPER 

The  production  of  paper  was  for  many  years  an  art,  especially 
during  that  period  before  the  paper  machine  came  into  general 
use.  It  is  obvious,  therefore,  that  in  the  past  the  quality  of  paper 
was  judged  and  determined  by  empirical  methods  and  esthetic 
standards  which  were  in  many  cases  crude  from  a  scientific  point 
of  view.  It  is  true  that  an  experienced  man  may  determine 
much  in  regard  to  a  sheet  of  paper  by  tearing  it,  by  examining 
the  finish  or  surface,  and  by  looking  through  the  sheet  toward 
the  light.  Yet  in  all  such  tests  the  individual  must  be  very 
experienced,  and  there  is  always  the  personal  factor  to  be 

considered. 

1.  PURPOSE  OF  TESTS 

The  use  of  scientific  or  technical  tests  on  paper  has  little  value 
unless  the  purpose  for  which  the  paper  is  to  be  used  is  taken  into 
consideration.  The  tests  described  in  this  circular  are  those 
which  have  been  found  effective  in  determining  the  relative  value 
of  various  grades  of  paper  and  are  given  in  their  present  state  of 
development.  These  tests  do  not  always  give  sufficient  data, 
but  their  accuracy  is  generally  within  the  variation  in  uniformity 
of  the  paper.  There  are,  however,  certain  qualities  of  paper 
that  it  is  difficult  to  define  or  record  numerically,  such  as  "  color," 
"finish,"  and  "formation."  These  three  qualities  are  often  the 
deciding  factors  in  the  purchase  of  paper,  especially  when  it  is 
not  bought  on  specifications.  It  is  therefore  important  to  develop 
in  the  near  future  methods  of  testing  these  qualities. 

2.  DEVELOPMENT  OF  TEST  METHODS 

In  the  beginning  of  the  development  of  paper-testing  methods 
at  this  Bureau  the  methods  used  by  foreign  laboratories  were  more 
advanced  and  standardized  than  those  in  this  country,  and  many 
of  the  former  were  adopted.  Since  then  various  new  methods 
and  improvements  have  been  developed  in  the  United  States, 
and  one  of  the  greatest  contributory  agencies  was  the  growth  of  a 
technical  association  in  the  paper  industry  It  is  true,  however, 
that  the  requirements  of  the  Government  for  various  grades  of 
paper  and  the  need  of  placing  these  purchases  upon  a  scientific 
basis  have  been  a  great  stimulus  at  this  Bureau  in  the  develop- 
ment of  the  technique  of  paper  testing.  The  large  number  of 
samples  tested  yearly  to  determine  whether  Government  pur- 
chases have  conformed  to  the  specifications  has  given  an  opportu- 
nity for  ascertaining  the  accuracy  and  suitability  of  the  methods, 


8  Circular  of  the  Bureau  of  Standards 

and  has  led  to  numerous  changes  and  to  the  adoption  of  new 
methods.  In  general,  it  is  necessary  to  develop  tests  for  paper 
for  a  specific  use.  This  is  illustrated  in  the  case  of  a  tearing  test, 
several  of  which  have  recently  appeared  in  print;  for  in  this  case 
it  was  essential  to  find  a  test  for  wrapping  paper  which  would 
reproduce  service  conditions  more  satisfactorily  than  with  a 
bursting  or  "pop  "  test.  In  regard  to  certain  other  tests,  such  as 
the  determination  of  the  amount  of  rosin  sizing  in  paper,  it  has 
been  possible  to  simplify  the  procedure  and  to  lessen  the  time 
required.  The  slight  decrease  in  accuracy  in  the  case  mentionec^ 
resulting  from  the  use  of  the  shorter  method,  limits  its  use  to 
routine  testing  but  conserves  material  and  saves  much  time.  It 
is  becoming  more  and  more  apparent  that  no  one  testing  device 
is  applicable  to  all  grades  of  paper,  and  it  will  be  necessary  to 
develop  instruments  for  determining  the  physical  qualities  of 
each  of  the  general  classes  of  paper.  This  is  illustrated  by  the 
fact  that  container  board  and  tissue  paper  have  different  uses, 
are  constructed  differently,  and  should  be  tested  differently. 
There  is  therefore  a  large  field  yet  to  be  developed,  not  only  in 
testing  instruments  but  also  in  methods  of  analysis.  Quality 
and  uniformity  depend  in  large  measure  upon  methods  of  deter- 
mining quality  and  uniformity,  and  such  methods  and  apparatus 
should  be  made  more  specific  and  refined. 

3.  SPECIFICATIONS 

It  is  becoming  increasingly  common  to  purchase  material  ac- 
cording to  an  agreement  between  the  purchaser  and  the  con- 
tractor which  is  based  on  the  value  of  the  material  for  the  purpose 
for  which  it  is  bought.  In  such  cases  it  is  customary  for  the  pur- 
chaser or  the  contractor  to  submit  specifications  of  the  material 
in  question,  which  specifications  are  agreed  upon  by  both  parties 
interested  before  the  purchase  is  ratified.  These  specifications 
may  be  a  vague  understanding  between  the  purchaser  and  the 
contractor,  they  may  be  a  very  indefinite  statement  of  the  merits 
of  the  material  in  question,  but  they  are  becoming  more  and 
more  to  be  based  on  scientific  and  technical  data. 

In  the  past,  in  the  development  of  specifications  for  material, 
little  attention  has  been  paid  to  any  particular  standard  for 
specifications,  it  being  probably  felt  that  each  man  or  concern 
knew  best  how  to  write  a  specification.  In  many  cases  this  led 
to  a  form  detrimental  to  the  purchaser,  the  contractor,  or  both. 
It  is  therefore  thought  that  consideration  should  be  given  to 
specifications  in  general,  which  can  then  be  specialized  to  meet 


The  Testing  of  Paper  9 

the  particular  case.  With  this  in  view,  a  brief  outline  is  herewith 
given  on  the  methods  of  preparing  paper  specifications.  This 
topic  is  not  here  treated  as  a  comprehensive  standardization  of 
the  method  of  preparation  of  specifications,  but  is  given  merely 
as  a  guide  to  the  preparation  of  specifications  in  a  field  in  which 
the  uses  of  specifications  are  still  in  the  process  of  development. 

(a)  FORMULATION. — During  the  process  of  formulation  of  the 
specifications    various    interested    contributory    agencies    should 
assist  in  revising  them  as  first  initiated.     These  specifications,  as 
revised,  should  be  finally  agreed  upon  by  the  interested  parties 
and  be  officially  authorized.     When  so  authorized  they  are  given 
a  certain  official  status,  whether  it  be  between  individuals,  com- 
panies, associations,  or  industries.     Care  is  to  be  taken  that  the 
scope  of  application  or  jurisdiction  of  the  specifications  be  made 
clear,  as  well  as  their  designated  or  implied  lifetime.     It  is  also 
very  desirable  to  include  standard  practice  for  revision  of  the 
specifications  and  also  a  standard  typography  and  format. 

(b)  NOMENCLATURE. — A  standard  terminology  should  be  adopted 
and  adhered  to   throughout  the  specifications.     When  possible 
references  and  authority  should  be  given.     Special  conditions  or 
limitations  as  to  terminology  should  be  included,  and  a  means  for 
a  decision  as  to  disputes  on  terminology  may  be  of  assistance. 

(c)  QUALITY  STANDARDS. — As  a  preliminary  to  the  specifications 
of  the  quality  of  the  material  to  be  purchased,  it  is  desirable  to 
name  exactly  and  define  the  material  in  question.     The  use  to 
which  the  material  specified  is  to  be  applied  should  be  considered 
in  great  detail.     It  is  then  necessary  to  have  a  qualitative  descrip- 
tion of  the  useful  properties  desired  and  a  statement  of  the  unde- 
sirable  properties.     The    quantitative    statement   of   the   useful 
properties,  composition,  dimensions,  form,  and  structure,  and  of 
harmful  or  nonuseful  properties,  giving  maxima  and  minima  per- 
missible, is  that  part  of  specifications  which  is  often  considered  most 
important.     It  is  necessary,  however,   to   include  a  qualitative 
and  quantitative  statement  of  tolerances  permitted  in  each  case. 

(d)  TECHNICAL  PRACTICE. — A  material  purchased  on  specifica- 
tions must  be  tested  in  order  to  determine  that  it,  on  delivery, 
conforms   to   the   specifications.     Inspection   and   sampling  are 
therefore  necessary.     Standard  test  methods  must  be  a  part  of  the 
specifications  and  naturally  include  a  description  of  the  test  instru- 
ments and  facilities  to  be  used.     Test  certificates  should  be  avail- 
able, the  results  properly  interpreted,  and  the  material  accepted,  re- 
jected, or  subject  to  further  test.     All  reports,  records,  and  original 
data  should  be  kept  in  available  form. 

22848°— 21 2 


io  Circular  of  the  Bureau  of  Standards 

III.  PHYSICAL  TESTING 

The  physical  qualities  of  paper,  such  as  dimensions,  weight, 
strength,  and  moisture  content,  are  affected  by  atmospheric 
changes  in  temperature  and  relative  humidity;  but  it  is  not  pos- 
sible, with  the  limited  information  available,  to  determine  the 
factors  necessary  to  reduce  the  data  obtained  at  one  temperature 
and  relative  humidity  to  that  which  they  would  be  at  another 
temperature  and  relative  humidity,  or  at  a  standard  atmospheric 
condition.  The  variation  caused  by  changes  of  temperature 
and  relative  humidity  is  not  constant  for  paper,  in  general,  and  is 
seldom  constant  within  a  restricted  class  of  paper.  In  order  to 
obtain  standard  conditions  in  which  to  test  the  physical  proper- 
ties of  paper  at  this  bureau,  a  large  room  has  been  equipped  with 
an  apparatus  (Fig.  i)  which  maintains  a  temperature  of  70°  F 
and  a  relative  humidity  of  65  per  cent.  These  conditions  have 
been  decided  upon  rather  arbitrarily,  yet  seem  advisable  for  the 
following  reasons:  It  is  relatively  easy  to  produce  the  conditions; 
it  is  an  atmosphere  in  which  it  is  not  uncomfortable  to  work;  these 
conditions  are  apparently  approximately  midway  in  the  increasing 
and  decreasing  curves  of  strength,  due  to  variation  of  temperature 
and  relative  humidity,  as  indicated  by  work  already  done;  and, 
lastly,  most  of  the  laboratories  which  control  testing  conditions 
have  adopted  70°  F  temperature  and  65  per  cent  relative  humidity 
as  their  standard  and  have  collected  their  test  data  under  those 
conditions.  Therefore,  all  samples  of  paper  tested  for  physical 
qualities  that  are  affected  by  atmospheric  changes  are  conditioned 
for  at  least  2  hours  in  this  room  before  being  tested.  They  are 
placed  on  a  rack  properly  fanned  out  in  order  that  as  much  of 
the  paper  may  be  exposed  as  possible.  (Fig.  2.) 

1.  WEIGHT 

For  convenience  in  laboratory  work,  a  ream  25  by  40  inches  in 
size  containing  500  sheets  (25X40 — 500)  has  been  adopted 
as  standard.  The  data  are  obtained  in  pounds  per  standard 
ream  and  are  then  converted  to  the  ream  size  required  for  the 
particular  sample  of  paper  in  question.  Ten  sheets  of  paper, 
each  io  by  io  inches  in  size,  are  weighed  on  a  quadrant  scale, 
illustrated  in  Fig.  3,  having  an  average  accuracy  of  approximately 
0.2  per  cent  between  20  and  no  and  a  maximum  error  of  0.5  per 
cent  between  the  same  points  on  the  scale.  There  are  several 
types  of  scales  or  weighing  devices  on  the  market  which  may  be 


The  Testing  of  Paper 


1 1 


FIG.   i. — Apparatus  for   maintaining   standard    atmospheric   conditions:  Temperature, 

70°  F,  and  relative  humidity,  65  per  cent 

This  apparatus  automatically  washes  the  return  air,  saturates  it  at  a  given  temperature,  and  then  raises 
the  temperature  cf  air  to  a  proper  point  so  that  standard  conditions  are  maintained  in  the  room 


FIG.  2. — Rack  for  conditioning  paper 

Samples  of  paper,  before  being  tested,  are  subjected  to  the  standard  conditions,  so  that  all  papersmay  be 
tested  under  the  same  conditions 


Circular  of  the  Bureau  of  Standards 


FIG.  3. — Scale  for  weighing  paper 
This  type  of  balance  is  used  for  laboratory  work  in  determining  the  ream  weight  of  paper 


FIG.  4. — Thickness  tester 
The  thickness  of  the  paper  is  read  off  on  a  dial  in  thousandths  of  an  inch 


The  Testing  of  Paper 


used  for  this  purpose.  It  is  obvious  that  the  samples  being 
weighed  must  be  accurately  measured  to  determine  their  size,  and 
this  is  done  by  means  of  an  accurate  rule,  graduated  in  tenths  of 
inches.  The  following  formula  is  of  assistance,  where  a  is  scale 
reading,  b  is  one  dimension  of  the  sample,  c  is  the  dimension  at 
right  angles  to  b,  and  d  is  the  number  of  sheets  of  paper  in  the 
sample : 


ax  1000 

bxc  Xd 


weight  in  pounds  per  ream  25  X4O — 500. 


For  samples  of  paper  weighing  less  than  20  on  the  quadrant  scale 
a  chemical  balance  is  used.  For  convenience,  the  following 
formula  is  used : 

(Weight  in  grams)  X  (1.102)  X  (1000)  .        . 

(Area  of  sample  in  square  inches)  X  (number  of  sheets) 

pounds  per  ream  25X40 — 500.  To  convert  the  weight  of  the 
standard  ream  to  the  weight  of  a  ream  of  the  desired  trade  size, 
it  is  only  necessary  to  multiply  the  weight  of  the  former  by  the 
area  of  the  latter  and  divide  by  1000,  provided,  of  course,  that 
the  latter  ream  contains  500  sheets.  This  is  illustrated  in  Table  3. 

TABLE  3.— Typical  Equivalent  Weights  in  Standard  and  Trade  Sizes 


Weight  of  ream, 
25  X  40  —  500 

Trade  size  ream, 
500  sheets 

Area  of  sheet 

Weight  of 
ream,  trade 
size 

Pounds 

Inches 

Inches  = 

Pounds 

52.6                      25X38 

950.0 

50 

64.2 

17X22 

374.0 

24 

100.0 

20X25 

500.0 

50 

156.0 

22.5X28.5 

641.3 

100 

This  scale  may  be  calibrated  by  placing  small  accurate  weights  in 
the  pan  and  taking  readings  on  the  scale.  An  average  of  several 
readings  at  uniform  distances  apart  on  the  scale  should  be  obtained. 

2.  THICKNESS 

There  are  a  number  of  instruments  or  devices  available  for  de- 
termining the  thickness  of  paper.  They  are,  usually,  a  spring 
micrometer  with  the  dial  graduated  into  thousandths  of  an  inch, 
as  shown  in  Fig.  4.  It  is  not  advisable  to  take  readings  much 
closer  than  half  of  one-thousandth  (0.0005)  of  an  inch.  Some  diffi- 
culty is  experienced  at  times  with  the  spring  of  the  micrometer,  and 
the  needle  or  pointer  should  be  adjusted  to  zero  whenever  it  does  not 


14  Circular  of  the  Bureau  of  Standards 

properly  return  there.  The  thickness  tester  is  calibrated  by  means 
of  standard  sheet  metal  leaf  gages.  Since  the  spring  is  not  com- 
pressed to  any  great  extent  when  testing  most  grades  of  paper,  the 
error  introduced  by  varying  pressure  exerted  by  the  spring  against 
the  paper  is  not  great.  Thickness  test  is  made  on  each  of  the  10 
sheets  of  paper  of  which  the  test  sample  is  composed,  and  an 
average  is  obtained  which  is  reported  as  thousandths  of  an  inch. 

3.  BURSTING  STRENGTH 

The  bursting  strength  is  the  apparent  pressure  necessary  to 
burst  a  hole  in  a  sheet  of  paper,  when  the  pressure  is  exerted  against 
a  definite  area  and  the  sheet  is  held  taut  by  a  clamp.  There  are 
several  types  of  such  instruments  available,  but  there  seems  to  be 
no  definite  relation  between  the  data  obtained  with  them.  In  any 
case,  such  an  instrument  is  empirical  and  the  data  obtained  with 
any  one  machine  are  relative.  Various  factors  in  the  paper  influ- 
ence the  test,  such  as  kind  and  length  of  fiber,  type  or  formation, 
weight,  thickness,  etc.  One  of  the  most  important  factors  is  the 
stretch  or  elongation  of  the  paper  under  pressure  or  strain. 

The  type  of  instrument  used  at  this  time  at  this  Bureau  for  this 
test  is  one  in  which  a  handwheel,  actuating  a  piston,  forces  glycerin 
(glycerol)  against  a  flexible  diaphragm  which  transmits  the  pressure 
to  the  sheet  of  paper.  The  paper  is  held  in  place  by  an  annular 
ring  and  the  hydrostatic  pressure  within  the  chamber  is  indicated 
on  a  suitable  gage,  as  illustrated  in  Fig.  5.  A  test  is  made  on  each 
of  the  10  sheets  of  the  test  sample  and  an  average  of  the  gage  read- 
ings is  obtained.  It  is  of  considerable  value  in  comparing  the 
bursting  strength  of  various  samples  of  the  same  class,  but  of  differ- 
ent weight,  to  reduce  the  bursting  strength  to  a  unit  weight  basis. 
This  is  done  by  dividing  the  bursting  strength  by  the  weight  of  the 
standard  size  ream  (25X40 — 500),  and  the  result  or  ratio  when 
multiplied  by  100  is  reported  for  convenience  as  a  percentage. 

It  is  obvious  from  a  study  of  such  a  device  that  there  are 
several  factors  in  its  design  and  construction  that  may  influence 
the  value  of  the  test  and  the  data  obtained.  These  are  as  fol- 
lows: The  age  and  condition  of  diaphragm,  the  pressure  of  the 
clamp  (except  in  the  case  of  the  lever  clamp  type),  the  amount 
of  glycerin  in  the  cylinder,  the  speed  and  uniformity  of  rotation 
of  the  handwheel,  and  the  accuracy  of  the  gage.  The  flexible 
diaphragm  deteriorates,  whether  used  or  not,  when  exposed  to 
air  and  in  contact  with  the  glycerin,  and  is  renewed  every  month. 
In  this  connection  it  is  to  be  noted  that  the  area  of  the  diaphragm 
in  contact  with  the  paper  at  various  pressures  is  not  constant. 


The  Testing  of  Paper  15 

For  this  reason  all  results  are  recorded  and  reported  as  "points" 
(gage-scale  divisions),  rather  than  as  pounds  per  square  inch. 
Precaution  should  be  taken  to  be  sure  that  the  cylinder  is  full  of 
glycerin — that  is,  that  there  is  no  air  present  within  the  chamber, 
since  otherwise  the  results  are  not  reliable.  It  is  important 
that  the  handwheel  be  turned  at  a  uniform  rate,  and  1 20  rpm  has 
been  adopted  as  standard.  The  pressure  gage  is  calibrated 
ever}-  month  by  means  of  a  dead-weight  tester,  and  corrections 
applied  when  necessary. 


FIG.  5. — Bursting  strength  tester 

The  sample  of  paper  is  burst  by  means  of  pressure  exerted  through  a  rubber  diaphragm  which  conforms 
to  the  shape  of  the  paper 

4.  TENSILE  STRENGTH 

There  do  not  seem  to  be  any  instruments  of  American  manu- 
facture built  for  the  purpose  of  determining  the  tensile  strength 
of  paper.  The  apparatus  illustrated  in  Fig.  6  is  of  foreign  manu- 
facture and  is  used,  with  some  modifications,  for  testing  both 
paper  and  textiles.  A  strip  of  paper  15  mm  wide  is  clamped 
in  the  jaws,  so  that  the  distance  between  them  is  90  mm.  By 
means  of  a  piston,  hydraulically  operated,  the  lower  jaw  is  pulled 
away  from  the  upper  one,  and  the  lever  arm  with  the  weight  on 
the  end  is  brought  out  at  an  angle  until  rupture  of  the  paper 
takes  place.  A  ratchet  with  pawls  holds  the  arm  at  the  point 
on  the  scale  where  the  break  occurred.  This  scale  is  graduated 
in  fractions  of  kilograms  and  has  a  capacity  of  50  kg.  A  second- 
ary scale,  midway  up  on  the  lever  arm,  gives  the  elongation  of 
the  strip  of  paper  at  the  point  of  rupture. 


i6 


Circular  of  the  Bureau  of  Standards 


FIG.  6. — Tensile  testing  machine 


By  means  of  this  instrument  the  tensile  strength  of  paper  and  the  elongation  at  rupture  may  be  deter- 
mined 


The  Testing  of  Paper  1 7 

In  making  the  tensile  test  on  paper,  10  test  strips,  each  15  mm 
wide  and  150  mm  long,  are  carefully  cut  from  the  test  sample  in 
both  the  "machine"  and  "cross"  direction.  An  average  of  the 
results  is  obtained  and  is  generally  converted  into  pounds  per 
inch  of  width  of  sample  by  multiplying  by  the  factor  3.732.  A 
useful  strength  factor  is  obtained  by  reducing  the  tensile  strength 
to  the  "breaking  length,"  or  the  length  of  paper  which,  if  sus- 
pended by  one  end,  would  break  of  its  own  weight.  This  factor 
is  obtained  by  the  following  formula : 

Tensile  strength  in  pounds  per  inch 

width  X 13  889  ,  ' 

_„  .  , — ; —     — ; — ? — -  — r  =  Breaking  length  in  yards. 

Weight  in  pounds  of  ream  (25  X  40-500) 

There  are  several  factors  of  importance  to  be  considered  when 
operating  this  apparatus.  The  sample  should  be  properly  ad- 
justed in  the  jaws,  so  that  there  is  no  uneven  diagonal  strain  on 
the  strip  or  incorrect  alignment.  This  is  sometimes  difficult, 
as  the  upper  jaw  is  not  rigid.  The  test  strip  should  be  accurately 
cut  along  the  "machine"  direction  of  the  test  sample  or  at  right 
angles  to  that,  never  diagonally  across.  The  regulating  valve  of 
the  water  supply  should  be  adjusted  to  permit  a  downward  speed 
of  3  inches  per  minute  of  the  lower  jaw.  It  is  obvious,  however, 
that  if  two  papers  are  tested  at  the  same  rate  and  one  sample  has 
twice  the  percentage  stretch  of  the  other,  that  the  time  to  break  will 
differ  for  the  two  papers.  The  apparatus  is  calibrated  once  a  year 
by  hanging  accurate  weights  by  a  thread  or  light  string  from  the 
upper  jaw  and  determining  the  points  on  the  scale  which  should 
correspond.  The  difference  is  the  necessary  correction. 

5.  FOLDING  ENDURANCE 

The  folding  endurance  of  a  sample  of  paper  is  obtained  by  a 
machine  which  registers  the  number  of  alternate  folds  the  sample 
will  endure  before  breaking,  while  under  a  constant  tension  of  i 
kg.  The  test  strip,  15  mm  wide  and  90  mm  long,  is  placed  in  the 
jaws  and  the  apparatus  is  started.  The  strip  is  then  folded  flat 
upon  itself,  then  opened  and  folded  at  the  same  line  upon  itself 
in  the  reverse  direction,  this  being  called  a  double  fold.  The 
number  of  double  folds  the  sample  will  withstand  before  breaking 
is  indicated  on  a  dial  and  is  reported  as  the  folding  endurance. 
Five  tests  are  made  in  both  the  "  machine  "  and  "  cross  "  direction 
of  the  test  sample,  and  an  average  is  obtained.  A  speed  of  120 
double  folds  per  minute  is  maintained  by  means  of  a  small  electric 

22848°— 21 3 


i8 


Circular  of  the  Bureau  of  Standards 


motor.  This  tester  is  illustrated  in  Fig.  7.  It  is  to  be  noted, 
however,  that  the  folding  endurance  test  under  tension  seems  to 
be  more  affected  by  atmospheric  changes  of  temperature  and 
relative  humidity  than  most  of  the  physical  tests.  The  stretch 
of  the  paper  is  also  a  factor  influencing  the  test.  The  calibration 
and  standardization  of  the  folding  tester  require  much  attention, 
since  there  are  several  moving  parts  that  become  worn.  To 
obtain  check  results  on  different  machines,  it  is  necessary  to  check 


FIG.  7. — Folding  tester 

The  folding  endurance  of  paper  under  tension  is  determined  by  the  folding  of  a  strip  of  paper,  and  the 
number  of  double  folds  which  the  samples  will  resist  is  indicated  on  the  dial 

carefully  the  bearings,  rollers,  and  the  tension  of  the  springs,  and 
to  have  their  dimensions  all  accurately  the  same. 

6.  TEARING  STRENGTH 

A  method  of  determining  the  tearing  strength  of  paper  has 
become  of  considerable  importance,  and  a  number  of  devices  have 
been  proposed  for  this  purpose.  The  following  method  has  been 
adopted  tentatively  until  the  conclusion  of  further  work.  For 
this  test  the  tensile  testing  machine  as  shown  in  Fig.  8  has  been 
adapted,  with  the  weight  taken  from  the  lever  arm.  Ten  strips 


The  Testing  of  Paper 


FIG.  8. — Tearing  tester 

This  is  an  adapted  tensile  testing  machine  with  the  weights  removed  to  give  it  more  sensitiveness;  it 
is  used  for  tearing  a  strip  of  paper  in  determining  its  resistance  to  tear.  There  are  other  devices  being 
developed  for  this  purpose 


2O  Circular  of  the  Bureau  of  Standards 

i  inch  wide  are  slit  halfway  down  the  middle  and  each  half-inch 
end  is  placed  in  one  of  the  jaws,  the  lower  jaw  being  offset  one- 
half  inch  as  illustrated.  A  lineal  downward  speed  of  3  inches  per 
minute  of  the  lower  jaw  is  used,  and  the  tearing  strength  is  indi- 
cated as  points  on  the  scale.  The  apparatus  must  be  calibrated 
with  the  weight  off  the  lever  arm,  and  a  conversion  curve  may  be 
plotted  in  order  that  the  readings  from  the  scale  may  be  readily 
obtained  in  grams.  • 

Ten  tests  are  made  in  both  the  "machine"  and  "cross"  direc- 
tions, 10  sheets  being  used  in  each  test  to  obtain  an  average.  A 
maximum  tearing  strength  in  grams  is  obtained  by  this  method, 
and  the  average  of  the  10  tests  is  reported  as  such.  It  is  to  be 
noted  that  with  heavy  or  thick  samples  it  is  necessary  to  use  a 
smaller  number  of  sheets  in  each  test  sample,  as  there  is  a  tend- 
ency for  the  tearing  edges  to  rub  or  bind.  This  friction  has  been 
eliminated  to  a  considerable  extent  by  having  the  lower  jaw  offset, 
so  that  the  tearing  strain  is  parallel  to  the  test  strip.  This  test 
will  probably  be  modified  to  some  extent  in  the  near  future,  as  a 
maximum  value  is  not  ahvays  in  agreement  with  service  tests. 

7.  ABSORPTION 

There  are  several  methods  for  determining  the  absorbency  of 
bibulous  papers,  and  a  study  of  these  methods  is  now  in  progress 
to  determine  their  relations.  In  the  case  of  blotting  papers  the 
test  should  reproduce  service  conditions  as  much  as  possible, 
since  not  only  the  total  absorption  and  the  rate  are  important, 
but  also  the  effect  of  repeated  applications.  In  addition,  the 
effect  of  ink  in  place  of  water  during  the  test  is  to  be  considered. 
The  method  as  given  is  used  for  testing  the  absorption  of  blotting 
paper,  but  is  open  to  the  criticism  that  the  area  of  the  cross  section 
or  thickness  is  not  taken  into  consideration. 

In  making  this  test,  using  the  "strip"  method,  a  strip  of  blot- 
ting paper  15  mm  (about  three-fifths  inch)  wide  and  150  mm 
(about  6  inches)  long  is  suspended,  as  illustrated  in  Fig.  9,  so  that 
the  lower  end  dips  3  mm  (about  one-eighth  inch)  into  a  pan  of 
distilled  water.  Beside  the  strip  is  a  scale  reading  in  millimeters 
(fractions  of  inches),  and  at  the  end  of  each  minute  for  10  min- 
utes readings  are  taken  of  the  height  to  which  the  liquid  rises  in 
the  strip.  Five  tests  are  made  in  both  the  "machine"  and 
"  cross  "  direction  and  an  average  obtained.  The  result  is  reported 
as  the  height  to  which  the  liquid  will  rise  in  10  minutes.  When 
necessary,  or  advisable,  the  same  strips  may  be  subjected  repeat- 
edly to  the  test,  which  will  indicate  the  decreasing  ability  to  ab- 


The  Testing  of  Paper 


sorb  water  or  ink.     In  addition,  a  standard  ink  of  the  following 
formula  may  be  used : 


Tannic  acid 

Gallic  acid 

Ferrous  sulphate 

Dilute  hydrochloric  acid  (U.  S.  P.) 

Phenol 

Bavarian  blue,  S.  &  J.  No.  478  or  similar  suitable  dye  , 
Water  to  make  a  volume  of  loooccat  15. 6°  C. 


Grams 
23-4 

7-7 
30.  o 

25.0 

1.  o 

2.  2 


This  is  one 


FIG.  9.— Absorption  tester 

aethod  of  testing  blotting  paper,  and  the  height  of  rise  of  liquid  is  indicated  on  the  two  >. 
pies  of  paper,  one  on  either  side  of  the  metric  rule 


The  method  as  given  above  is  adopted  tentatively  and  will  be 
modified  or  changed  if  future  work  makes  it  advisable.  Other 
methods  have  been  suggested  and  are  being  investigated,  such  as 
the  method  when  water  or  ink  is  allowed  to  drop  from  a  i  cc 
pipette,  or  a  sample  is  totally  immersed  in  water  or  ink  for  a 
given  time  and  the  percentage  amount  absorbed  determined. 


22  Circular  of  the  Bureau  of  Standards 

8.  TRANSPARENCY 

It  sometimes  becomes  advantageous,  in  order  to  more  specific- 
ally evaluate  the  efficiency  of  two  or  more  samples  of  envelope 
windows,  tracing  paper  or  cloth,  glassine  paper,  etc.,  to  assign  a 
numerical  value  to  the  opacity  or  transparency  of  the  various 
samples.  This  is  particularly  advantageous  if  the  quality  of  two 


FIG.  10. — Transparency  apparatus 
This  is  used  for  determining  the  relative  transparency  and  opaqueness  of  papers 

similar  papers  is  so  nearly  alike  in  this  respect  as  to  be  indistin- 
guishable by  ordinary  observation. 

The  Bureau  has  developed  and  adopted  a  standard  method  for 
determining  the  transparency  of  paper  and  tracing  cloth,  which 
is  described  in  detail  in  B.  S.  Circular  No.  63  and  illustrated  in 
Fig.  10.  Briefly  this  method  consists  in  placing  a  sample  of  the 
paper  or  cloth  to  be  tested  over  two  adjacent  surfaces,  one  white 
and  the  other  black,  and  measuring  the  reduction  in  contrast  of 
the  appearance  of  the  two  surfaces.  If  the  material  in  question 


The  Testing  of  Paper  23 

is  quite  transparent,  the  contrast  between  the  black  and  white 
surfaces  as  seen  through  the  material  will  be  quite  noticeable; 
but  if  the  material  is  opaque,  none  of  the  light  incident  upon  its 
surface  will  be  transmitted  and  absorbed  by  the  black  surface 
beneath  and  consequently  there  will  be  no  contrast  between  the 
parts  of  the  material  covering  the  black  and  white  surfaces. 

In  making  the  measurements  one  must  use  a  photometer  having 
a  divided  photometric  field,  one-half  of  which  is  illuminated  by 
the  light  coming  from  the  material  over  the  white  surface,  while 
the  other  half  is  illuminated  by  the  light  coming  from  the  mate- 
rial over  the  black  surface.  The  two  halves  of  the  photometric 
field  are  then  "matched"  by  visual  observation  and  properly 
setting  the  photometer,  and  the  indicated  results  are  recorded. 
A  simple  computation  based  on  these  observations  gives  the  nu- 
merical measurement  sought,  which  is  called  the  "contrast 
ratio."  This  varies  between  zero  and  unity,  larger  values  indi- 
cating less  transparency. 

IV.  CHEMICAL  TESTING 

The  testing  of  paper  to  determine  those  constituents,  other  than 
fibrous  materials,  which  may  be  harmful  in  excessive  amounts  is 
desirable,  and  for  routine  testing  this  is  relatively  simple.  These 
constituents  usually  consist  of  sizing  material,  such  as  rosin, 
glue,  or  starch,  and  loading  materials  or  fillers,  such  as  clay,  talc, 
and  various  other  inert  substances.  There  are  other  materials 
present  in  certain  special  papers  which  are  not  considered  here. 

1.  LOADING  MATERIAL 

The  determination  of  the  amount  of  ash  of  the  paper  indicates 
the  absence  or  presence  of  loading  material,  which  is  usually 
added  for  the  purpose  of  giving  the  paper  a  smooth  printing  sur- 
face. Paper  having  an  ash  of  less  than  1.5  per  cent  usually  has 
not  had  a  filler  added.  In  the  case  of  all-rag  papers  the  ash  may 
be  as  low  as  0.5  per  cent,  while  with  papers  made  from  wood  pulp 
it  may  be  as  low  as  0.75  per  cent.  An  ash  greater  than  1.5  per 
cent  usually  indicates  that  some  loading  or  coating  material  has 
been  added,  except  where  old  papers  were  used,  or  a  pigment  dye 
for  coloring.  The  percentage  of  ash  obtained  includes  nonvolatile 
and  noncombustible  materials  from  several  sources,  as  follows: 
(a)  Ash  due  to  residual  minerals  in  fibrous  pulps,  (6)  ash  due  to 
loading  material,  (c)  ash  due  to  surface  coating,  and  (d)  ash  due 
to  mineral  coloring  materials  or  pigments  and  a  slight  residue 
from  sizing. 


24  Circular  of  the  Bureau  of  Standards 

A  i  -gram  sample  of  the  paper,  obtained  by  taking  equal  portions 
from  each  of  the  10  sheets  of  the  test  sample,  is  weighed  and  placed 
in  a  nickel  crucible.  This  is  placed  in  an  inclined  position  upon  a 
triangle  over  a  Bunsen  burner,  as  illustrated  in  Fig.  1 1 .  The 
paper  first  scorches,  then  carbonizes  and  finally  ignites.  When  the 
paper  begins  to  burn,  the  crucible  is  removed  from  the  flame  and 
the  paper  is  allowed  to  burn  quietly.  During  the  burning  care 
must  be  taken  that  none  of  the  ash  is  lost  by  air  currents.  To 
prevent  this  a  cover  may  be  placed  partially  over  the  crucible. 
After  the  burning  is  complete  the  crucible  is  then  replaced  on  the 


FIG.  n. — Means  of  determining  the  loading  in  paper 

This  illustrates  a  convenient  way  of  determining  the  ash  in  paper  when  there  are  many  samples  daily, 
and  shows  the  various  positions  of  crucibles  during  the  operation 

triangle  and  the  heat  applied  until  the  last  traces  of  carbon  have 
disappeared.  In  some  cases  it  is  necessary  to  use  a  blast  lamp  to 
consume  the  last  traces  of  carbon.  After  the  crucible  has  cooled 
the  ash  is  transferred  to  a  counterpoised  aluminum  pan  and 
weighed.  The  result  is  obtained  directly  as  a  percentage.  For 
extremely  accurate  work  the  moisture  in  the  paper  should  be  elimi- 
nated by  drying  at  100  to  105°  C  before  weighing  out  the  sample 
for  test,  and  the  ash  in  the  crucible  should  be  cooled  in  a  desiccator, 
as  a  variation  of  2  per  cent  in  moisture  content  will  give  an  error 
of  0.02  per  cent  for  each  per  cent  of  ash. 


The  Testing  of  Paper  25 

To  determine  the  kind  of  loading  or  coating  material  used,  it  is 
necessary  to  test  the  ash  qualitatively,  for  which  purpose  at  least 
o.2g.  of  ash  is  desirable.  Briefly,  tests  should  be  made  for  the 
substances  indicated  in  Table  4,  in  which  are  also  given  the  fillers 
that  the  presence  of  these  substances  would  indicate. 

TABLE  4.— Paper  Fillers  and  Their  Indicators 


Substance  sought 

Filler  indicated 

Calcium  carbonate  

Chalk 

Barium  sulphate  
Magnesium  silicates  

Blanc  file 
Talc 

Aluminum  silicates  

China  clay 

These  fillers  have  various  trade  names  and  do  not  in  all  cases 
have  definite  chemical  formulas,  but  the  presence  of  any  great 
amount  of  any  of  the  materials  in  the  first  column  would  indicate 
the  kind  of  filler  used,  and  further  confirmatory  tests  may  be 

made. 

2.  SIZING 

Nearly  all  grades  of  paper,  except  blotting,  filter,  and  similar 
papers,  have  a  sizing  material  added  to  give  certain  properties  to 
the  paper,  including  ink  resistance.  The  sizing  material  is  added 
during  the  preparation  of  the  stock  for  the  paper  machine  and, 
in  some  cases,  is  added  after  the  paper  is  made  by  passing  the 
sheet  through  a  bath  or  tub  containing  glue,  treated  starches,  or 
other  similar  material.  In  the  first  case  rosin  is  used,  and  the 
paper  is  said  to  be  "engine-sized";  in  the  latter  case  the  paper  is 
"tub-sized."  It  is  desirable  to  determine  the  presence  and 
amount  of  these  sizing  materials,  and  this  is  done  by  chemical 
analysis.  It  is  not  necessarily  true  that  the  percentage  of  sizing 
material  will  indicate  the  resistance  of  the  paper  to  ink;  for  this 
purpose  other  methods  are  being  developed. 

(a)  TOTAL  RESINS. — The  following  methods  are  used  for  de- 
termining total  resins:  Five  grams  of  paper  are  cut  in  strips 
about  one -half  inch  wide  from  the  10  sheets  of  the  test  sample  and 
are  folded  into  numerous  small  crosswise  folds.  These  are  placed 
in  the  siphon  cups  and  acidulated  alcohol  (900  cc  of  95  per  cent 
alcohol,  95  cc  distilled  water,  and  5  cc  glacial  acetic  acid)  is  poured 
into  the  cup  until  it  starts  to  siphon  over.  \Vhen  this  has  entirely 
siphoned  over  into  the  shell-shaped  extraction  flasks,  approxi- 
mately 20  cc  more  of  the  acidulated  alcohol  is  added  to  the  siphon 


26 


Circular  of  the  Bureau  of  Standards 


cup,  which  is  then  hung  on  the  condenser,  as  illustrated  in  Fig.  12. 
The  flask  is  set  into  the  steam  bath  and  the  extraction  proceeds 
for  about  2  hours,  or  until  the  cup  has  filled  and  siphoned  over 
about  ten  times.  The  extract  is  poured  into  a  weighed  glass  dish 
and  the  flask  washed  out  with  a  small  portion  of  the  acidulated 
alcohol,  which  is  added  to  the  original  extract.  The  alcohol  is 
then  evaporated,  the  dish  dried  and  weighed,  and  the  increase  in 
weight  of  the  dish  divided  by  5  will  give  the  percentage  of  total 
resins. 


FIG.  12. — Rosin  sizing  extractor 

This  illustrates  a  convenient  form  of  apparatus  for  determining  the  amount  of  rosin  sizing  in  paper  and 
shows  the  type  of  extraction  thimbles  and  condensers.  The  chief  criticism  of  this  is  that  it  is  difficult  to 
save  the  solvent,  and  where  expensive  solvents  are  used  this  form  is  not  practical 

For  additional  accuracy  other  than  for  routine  testing  or  con- 
trol work,  the  following  additional  method  is  advisable: 

Just  before  the  extracted  total  resins  in  the  glass  evaporating 
dish,  in  the  method  given  above,  go  to  dryness,  they  are  cooled 
and  taken  up  with  25  cc  of  ether,  and  transferred  to  a  250  cc 
separatory  funnel  containing  100  cc  of  distilled  water  and  25  cc  of 
a  saturated  solution  of  sodium  chloride,  the  latter  being  present 
to  prevent  the  formation  of  an  emulsion.  The  funnel  is  shaken 
thoroughly  and  the  contents  allowed  to  separate.  The  water  is 
drawn  off  into  a  second  separatory  funnel,  and  this  is  washed 


The  Testing  of  Paper  27 

again  with  25  cc  of  ether.  The  two  ether  extracts  are  combined 
and  washed  two  or  three  times  with  100  cc  of  distilled  water  to 
remove  all  the  salt  and  foreign  matter  other  than  ether-soluble 
resins.  Should  glue  which  is  extracted  from  the  paper  by  the 
alcohol  interfere  by  emulsifying  with  the  ether,  it  may  readily  be 
removed  by  adding  a  strong  solution  of  sodium  chloride  to  the 
combined  ether  extracts,  shaking  thoroughly  and  draining  it  off, 
repeating  if  necessary  before  washing  with  distilled  water.  The 
washed  extract  is  transferred  to  a  weighed  glass  dish,  evaporated 
to  dryness  slowly,  dried  in  an  oven  at  95  to  100°  C  for  one-half 
hour,  cooled,  and  weighed.  The  increase  in  weight  of  the  dish 
divided  by  5  will  give  the  percentage  of  total  resins. 

A  qualitative  test  for  rosin  may  be  made  by  the  following 
method:  A  small  portion  of  the  paper  boiled  with  5  cc  of  acetic 
anhydride  in  a  test  tube,  cooled,  and  treated  with  a  few  drops  of 
concentrated  sulphuric  acid  added  so  as  to  slip  smoothly  down  the 
side  of  the  test  tube,  will  develop  a  pink  ring  if  rosin  is  present. 
The  cover  of  a  porcelain  crucible  may  also  be  used,  and  in  this 
case  a  drop  or  two  of  each  of  the  liquids  are  brought  together  by 
glass  rods.  A  pink  color  may  develop  where  the  two  come  together. 

(6)  STARCH. — Starch  is  present  to  some  extent  in  some  papers, 
and  this  may  be  indicated  by  placing  a  few  drops  of  a  pale  yellow 
dilute  solution  of  iodine  in  potassium  iodide  on  the  sample  of 
paper.  The  development  of  a  blue  color  indicates  the  presence 
of  starch.  If  it  is  possible  to  extract  a  sufficient  amount  of  the 
starch  from  the  paper  by  warming  with  water,  a  few  drops  of  the 
solvent  containing  the  starch  is  placed  on  a  slide,  dried,  and 
examined  under  the  microscope.  In  this  way  the  kind  of  starch 
used  may  be  determined  by  the  shape  and  markings  of  the 
granules,  provided  the  starch  was  not  sufficiently  cooked  to  de- 
stroy the  grains.  For  the  quantitative  test  for  starch,  the  starch 
may  be  converted  into  dextrose  by  treating  a  few  grams  of  paper 
in  water  with  dilute  sulphuric  acid  and  estimating  the  amount  of 
dextrose  present  in  the  extract  by  Fehling's  solution. 

(c)  GLUE. — The  presence  of  glue  in  paper  may  be  indicated  by 
either  of  the  following  methods:  (i)  The  extract  obtained  by 
boiling  i  g  of  paper  in  water  is  decanted  into  a  test  tube,  cooled, 
and  treated  with  a  few  cc  of  ammonium  molybdate  solution, 
followed  by  a  few  drops  of  nitric  acid.  The  presence  of  glue  is 
indicated  by  a  white  amorphous  precipitate.  (2)  The  extract  ob- 
tained by  boiling  i  g  of  paper  in  water  is  decanted  into  a  test 
tube,  cooled,  and  treated  with  a  few  cc  of  tannic  acid  solution  of 


28  Circular  of  the  Bureau  of  Standards 

5  per  cent  concentration.  The  presence  of  glue  is  indicated  by  a 
heavy  flocculent  precipitate,  which,  when  heated,  becomes  co- 
agulated and  hard. 

Glue  may  be  determined  quantitatively  by  treating  3  to  5 
grams  of  paper  by  the  Kjeldahl  method  and  thus  determining  the 
amount  of  nitrogen  present.  The  percentage  of  nitrogen  obtained 
multiplied  by  5.6  will  give  the  percentage  of  glue  in  the  sample  of 
paper.  This  test,  however,  is  of  no  value  when  both  glue  and 
casein  are  present,  since  both  contain  nitrogen. 

V.  MICROSCOPICAL  TESTING 

In  the  examination  of  paper  to  determine  its  quality,  it  is  neces- 
sary to  have  a  means  of  identif ying  the  fibrous  materials  from  which 
the  paper  is  made,  since  some  fibers  do  not  deteriorate  as  rapidly  as 
others.  These  materials  are  chiefly  as  follows:  Rags;  chemical 
wood  pulp,  consisting  of  coniferous  and  deciduous  or  broad-leaf 
woods;  mechanical  or  ground-wood  pulp;  manila  and  jute;  and 
straw.  These  occur  in  some  cases  separately  but  more  often  in 
combination.  In  addition  to  identifying  the  presence  of  these 
various  fibrous  materials,  it  is  necessary  to  determine  the  amount 
of  each  present  in  the  paper.  Since,  however,  the  determination 
of  rag  in  a  paper,  for  instance,  does  not  indicate  the  grade  of  rag 
used  in  the  manufacture  of  the  paper,  specifications  built  up 
primarily  about  the  fiber  content  of  the  paper  are  not  always  the 
best. 

1.  PROCEDURE 

It  is  important  to  obtain  a  representative  sample,  and  for  that 
reason  a  small  corner,  about  as  large  as  a  penny,  of  each  of  the  10 
sheets  of  the  test  sample  is  cut  off  and  torn  into  small  pieces. 
These  are  placed  in  a  50  cc  beaker  and  approximately  20  cc  of  a 
0.5  per  cent  solution  of  caustic  soda  is  added.  The  beaker  is  placed 
on  a  hot  plate  or  stove  and  brought  to  a  boil,  but  the  boiling  is 
not  continued  for  more  than  a  minute  or  two.  The  liquor  is 
drained  off  and  the  pieces  of  paper  are  washed  several  times  with 
tap  water,  care  being  taken  that  none  are  lost.  They  are  then 
w ashed  with  approximately  20  cc  of  0.5  per  cent  solution  of  hydro- 
chloric acid,  and  then  washed  twice  more  with  tap  water.  A 
portion  of  the  small  pieces  is  rolled  between  the  fingers  into  a  pill 
about  the  size  of  a  small  pea  and  transferred  to  a  test  tube,  which 
is  half  filled  with  water.  The  test  tube  is  placed  in  a  shaking 
machine,  as  illustrated  in  Fig.  13,  and  shaken  until  the  paper  is 
disintegrated  into  fibers,  which  normally  takes  about  one-half 
minute.  By  means  of  a  glass  tube  of  about  5  mm  internal  diameter 


The  Testing  of  Paper 


29 


FIG.  13.— Test  tube  shaker 

This  device  quickly  disintegrates  the  samples   of  paper  into  fibers  and  eliminates  all  th< 
doing  it  laboriously  by  hand 


necessity  of 


30  Circular  of  the  Bureau  of  Standards 

a  representative  amount  of  the  fibers  is  transferred  to  a  glass  slide 
and  the  water  removed  by  placing  several  thicknesses  of  hard 
filter  paper  on  either  side  of  the  slide.  After  the  excess  water  has 
been  thus  removed,  a  strip  of  filter  paper  is  placed  on  the  fibers  to 
absorb  any  traces,  leaving  the  fibers  dry  but  not  so  dry  that  there 
will  be  difficulty  in  separating  them.  Two  or  three  drops  of  the 
zinc-chloride-iodine  stain  described  below  are  placed  on  the  fibers, 
which  are  teased  out  with  steel  needles  until  the  fibers  are  reason- 
ably uniformly  distributed  and  free  from  knots  of  fibers. 

COMPOSITION  AND  PREPARATION  OF  ZIXC-CHLORIDE-!ODINE  STAIN  2 

25  cc  saturated  zinc  chloride  solution  at  70°  F 
5.25  g  potassium  iodine 
0.25  g  iodine 
.2.5  g  distilled  water 

The  three  last  ingredients  are  mixed  together  and  the  zinc  chloride 
added.  The  insoluble  matter  is  allowed  to  settle  at  least  overnight  and 
the  supernatant  liquid  is  decanted  off.  The  stain  must  be  kept  in  the 
dark  or  in  a  bottle  opaque  to  light.  It  may  be  made  up  in  larger  quanti- 
ties, provided  it  is  kept  from  the  light  and  air. 

After  the  fibers  are  properly  teased  out  with  the  needles,  another 
but  thinner  glass  slide  is  placed  on  top  of  the  first  slide,  and  the 
excess  stain  is  squeezed  out  and  absorbed  by  blotting  paper.  The 
slide  is  now  ready  for  the  microscope,  which  is  of  the  binocular  type, 
using  artificial  illumination  as  indicated  in  Fig.  14,  and  having  a 
magnification  of  about  50  diameters.  Care  must  be  observed  to 
keep  the  slide  away  from  the  light  before  using  it  for  the  estimation, 
and  in  any  case  the  estimation  should  be  made  at  least  within 
one  hour  from  the  time  the  slide  was  made  up.  Under  the 
microscope,  using  the  zinc-chloride-iodine  stain,  the  fibers  appear 
colored,  as  follows: 

Cotton  and  linen  rags 1 

Cooked  and  bleached  manila }Wme  red 

Cooked  and  bleached  wood  pulp ] 

Ccoked  and  bleached  straw  and  esparto  |Blue  to  blue  ™let 
Mechanical  or  ground  wood  pulp..] 

Jute,  uncooked,  and  manila ^Yellow  to  lemon  yellow 

Highly  lignified  fibers J 

In  making  the  estimation  both  the  distinctive  shape  and  mark- 
ings of  the  fibers,  as  well  as  the  colors  as  developed  by  the  zinc- 
chloride-iodine  stain,  are  of  importance.  Extreme  care  must  be 
observed  to  have  all  beakers,  test  tubes,  needles,  and  even  fingers 
free  from  any  fibrous  material  before  beginning  the  preparation  of 
a  sample  or  slide. 

2 This  formula  is  tentative.    Its  value  is  subject  to  a  number  of  factors  that  are  now  being  studied. 
Additional  information  may  be  obtained  from  the  paper  section,  Bureau  of  Standards. 


The  Testing  of  Paper  31 

2.  ESTIMATION 

For  general  work  and  routine  testing,  the  estimation  method 
has  been  adopted.  This  consists  primarily  of  properly  judging  or 
estimating  the  relative  proportions  of  fibers  present,  after  studying 
various  fields  of  the  slide.  For  this  purpose  standard  samples  of 
known  content  are  essential,  and  there  are  available  here  most  of 
the  more  common  commercial  mixtures  of  fibrous  materials,  made 
up  under  rigid  conditions.  Since  the  accuracy  of  this  method 
depends  largely  on  the  experience  of  the  operator,  and  since  there 


FIG.  14. — Binocular  microscope  and  daylight  lamp 

For  estimating  and  examining  fibers  it  is  desirable  to  have  constant  light  conditions,  and  the  use  of  a 
binocular  microscope  is  of  assistance  when  there  is  much  continuous  estimating  work 

is  a  tendency  to  judge  or  estimate  by  appearance  or  area,  it  is 
most  necessary,  even  for  the  experienced  operator,  to  refer  in  many 
cases  to  the  standard  samples.  This  is  especially  true  in  the  case 
of  ground  wood,  since  the  specific  gravity  of  this  material  is  not 
the  same  as  that  of  rag  pulp  or  chemical  wood  pulp,  and  if  standard 
samples  are  not  used  low  estimations  are  obtained.  It  is  to  be 
noted  that  the  percentage  of  various  fibrous  materials  present  is 
given  on  the  basis  of  the  total  fiber  content  alone  and  nonfibrous 


32  Circular  of  the  Bureau  of  Standards 

materials  are  not  considered.  There  are  other  methods  besides 
the  one  given  for  determining  the  amounts  of  various  fibrous 
materials  in  paper,  but  most  of  these  are  not  sufficiently  rapid  for 
routine  testing,  and  it  is  a  question  whether  their  accuracy  is 

much  greater. 

3.  MICROPHOTOGRAPHY 

It  is  often  necessary  to  have  a  permanent  record  of  the  fiber 
content  of  paper  and  also  to  have  an  opportunity  of  studying  the 
characteristics  of  the  various  fibers.  For  this  purpose  a  com- 
plete photomicrographical  equipment  is  available,  and  Figs.  15, 
1 6,  17,  and  18  illustrate  the  distinctive  markings  of  various  fibers. 
This  field  of  research  has  not  yet  been  sufficiently  developed,  but 
it  opens  considerable  opportunity.  The  methods  employed  are 
those  commonly  used  with  such  equipment,  except  that  a  2o-foot 
bellows  permits  of  a  flatter  field  on  the  photographic  plate  and 
greater  definition.  The  iise  of  monochromatic  light  is  also  of 
great  assistance. 

VI.  BIBLIOGRAPHY 

Most  of  the  data  and  information  on  paper  testing  have  been 
published  as  articles  in  magazines  and  periodicals.  The  books 
referred  to  are  those  most  available  at  the  present  time.  The 
periodicals  given  are  those  of  greatest  circulation  with  the  technical 
men  of  the  industry,  but  there  are  others  containing  at  intervals 
articles  on  paper  testing.  The  results  of  investigations  of  Gov- 
ernment laboratories  have  generally  been  published  in  the  trade 
periodicals.  Reference  is  also  made  to  the  secretary  of  the  Tech- 
nical Association  of  the  Pulp  and  Paper  Industry  at  542  Fifth 
Avenue,  New  York  City,  N.  Y. 

i.  BOOKS 

Sindall,  R.  W.,  Paper  technology,  253  pp.,  13  plates,  158  illustrations;  1906.  Lon- 
don, Charles  Griffin  &  Co.  An  elementary  manual  on  the  manufacture,  physical 
qualities,  and  chemical  constituents  of  paper  and  of  paper-making  fibers. 

Cross,  C.  F.,  and  E.  J.  Bevan,  A  text-book  of  papermaking,  507  pp.,  16  plates,  99 
illustrations,  9  pp.  bibliography;  1916.  London,  E.  and  F.  N.  Spon  (Ltd.).  Contains 
a  chapter  on  paper  testing. 

Herzberg,  Wilhelm,  Papierpriifung  ( Paper  testing),  146  pp.,  65  cuts,  16  plates;  1902. 
Berlin,  Verlag  von  Julius  Springer.  An  introduction  to  the  study  of  paper. 

Klemm,  Paul,  Handbuch  der  Papierkunde  (Handbook  of  paper  technology)  oo,  4  pp., 
130  cuts,  3  colored  plates;  1910.  Leipzig,  Th.  Grieben's  Verlag.  With  references 
and  instructions  concerning  the  use,  manufacture,  testing,  and  selling  of  paper. 

2.  PERIODICALS 

Paper,  Paper  (Inc.),  251  West  Nineteenth  St.,  New  York  City,  N.  Y. 
Paper  Trade  Journal,  Lockwood  Trade  Journal  Co.,  10  East  Thirty-ninth  St.,  New 
York  City,  N.  Y. 


The  Testing  of  Paper 

\,   \ 


33 


FIG.  15. — Microphotograph  of  Douglas  spruce  fiber  (Pseudatsuga 
taxifolia).     X  100 


FIG.  16. — Micro  photograph  of  sugar  or  hard  maple  fih 
(Acersaccharum}.     X  100 


Circular  of  the  Bureau  of  Standards 


—Microphotograph  of  fibers  from  rag  pulp.      X  loo 


FIG.  18. — Micro  photo  graph  of  spruce  ground  wood  fiber  (Picea 
canadensis}.      X  TOO 


The  Testing  of  Paper  35 

The  Paper  Industry,  E.  B.  Fritz,  publisher,  356  Monadnock  Block,  Chicago,  111. 

Pulp  and  Paper  Magazine  of  Canada,  Industrial  and  Educational  Publishing  Co. 
(Ltd.),  Garden  City  Press,  St.  Anne  de  Bellevue,  P.  Que.,  Canada. 

N.  B. — For  reference  to  special  articles  on  paper  testing  appearing  in  these  period- 
icals, the  Committee  on  Paper  Testing  and  the  Committee  on  Bibliography,  both  of 
the  Technical  Association  of  the  Pulp  and  Paper  Industry,  542  Fifth  Avenue,  New 
York  City,  N.  Y.,  and  the  Bureau  of  Standards,  Washington,  D.  C.,  should  be  con- 
sulted. 

3.  GOVERNMENT  PUBLICATIONS 

The  testing  of  materials,  B.  S.  Circular  No.  45,  89  pp.;  1913.  Washington,  Govern- 
ment Printing  Office.  Contains  description  of  tests  made  on  paper,  see  pp.  59-62. 

Specifications  and  tests  for  transparency  of  paper  and  tracing  cloth,  B.  S.  Circular 
No.  63,  8  pp.;  1917.  Washington,  Government  Printing  Office. 

Sammit,  C.  Frank,  A  measurement  of  the  translucency  of  paper,  Department  of 
Agriculture,  Bureau  of  Chemistry  Circular  No.  96,  3  pp. ;  1912.  Washington,  -Govern- 
ment Printing  Office. 

Sammit,  C.  Frank,  The  detection  of  faulty  sizing  in  high-grade  papers,  Depart- 
ment of  Agriculture,  Bureau  of  Chemistry  Circular  No.  107,  3  pp.;  1913.  Washing- 
ton, Government  Printing  Office. 

Surface,  Henry  E-,  Bibliography  of  pulp  and  paper  industries,  Department  of 
Agriculture,  Forest  Service  Bulletin  No.  123,  Forest  Products  Laboratory  Series,  48 
pp.;  1913.  Washington,  Government  Printing  Office. 

VII.  REGULATIONS  REGARDING  TESTS 

The  Bureau  is  equipped  to  make  complete  examination  of 
papers  for  Government  offices  or  bureaus,  and  will,  in  its  discre- 
tion, perform  similar  service  for  the  general  public,  when  asked 
to  act  as  referee  or  where  the  nature  of  the  case  calls  for  an  au- 
thoritative test.  The  Bureau  thus  reserves  the  right  to  accept 
or  decline  requests  for  tests,  depending  upon  the  conditions  in  each 
instance. 

In  order  that  the  user  may  more  correctly  judge  a  paper  and 
determine  its  usefulness  for  the  purpose  intended,  he  should  be 
informed  upon  the  following  points  : 

(a)  Weight  per  standard  ream 
(6)  Thickness 

(c)  Bursting  strength 

(d)  Tensile  strength 

(e)  Folding  endurance 
(/")  Tearing  strength 
(g)  Absorption 

(h)  Amount  and  kind  of  loading  material 
(t)   Amount  and  kind  of  sizing  material 
( ;')   Fiber  composition 

1.     FEES 

All  tests  for  the  National  and  State  Governments  are  made  free 
of  charge.  For  municipal  governments  and  private  parties 
charges  are  made  according  to  nature  and  extent  of  the  work 


36  Circular  of  the  Bureau  of  Standards 

required.  Where  such  tests  are  accepted  the  fees  will,  in  general, 
be  based  upon  the  following  schedule,  which  states  the  fee  for 
each  test  on  a  single  sample  and  the  charge  for  the  same  test  on 
each  additional  sample,  where  several  are  submitted  at  the 
same  time. 

FEE  SCHEDULE  212.— Paper  Materials 


Test 

First 
sample 

Each 
additional 

2120. 
2I2b. 
2I2C. 
2I2d. 
2126. 
2I2f. 

2i2g. 

2I2&. 
2121. 
2I2J. 

Weight  determination  

$ 

:.  oo 

•5° 

:  oo 

.  00 
.  00 
.  00 
.  00 
.  00 

-5° 
5.00 

$C 

•75 

5° 
75 

5° 
50 
5° 
5° 
5° 

00 
CO 

Thickness  determination  
Bursting  strength  test  

Tensile  strength  test  

Folding  endurance  test  
Tearing  strength  test  
Absorption  test  
Ash  content  determination  
Total  resin  determination  

Fiber  composition  determination  

All  samples  of  paper  should  be  put  up  for  shipment  carefully 
protected  by  cardboard  or  other  material  to  insure  arrival  in  good 
condition.  All  paper  samples  themselves  should  be  plainly 
marked  "For  Paper  Section,  Bureau  of  Standards,  Washington, 
D.  C." 

A  careful  record  should  be  kept  by  the  sender,  so  that  the  identi- 
fication marks  may  be  used  in  the  certificate  to  avoid  repeating 
the  detailed  description  of  the  paper.  Samples  submitted  by 
Government  departments  should  be  marked  in  upper  left-hand 
corner  of  sheet  as  follows: 

Date —  Identification  marks. 

Submitted  by: 

Kind  of  paper, 

Item  number, 

Name  of  manufacturer, 

Tests  for  compliance  with  schedule, 

Remarks:  (Any  other  information  concerning  the  paper). 

Samples  submitted  by  private  parties,  mark  in  upper  left-hand 
corner  of  sheet  as  follows: 

Date —  Identification  marks. 

Submitted  by: 

Kind  of  paper, 

Use  of  paper, 

Ream  size  and  weight, 

Test  required , 

Remarks:  (Any  other  information  concerning  the  paper). 


The  Testing  of  Paper  37 

As  soon  as  the  fee  is  assigned  to  the  test,  a  bill  is  sent  at  once,  and 
payment  should  be  in  advance,  made  by  money  order  or  check 
drawn  to  the  order  of  the  "Bureau  of  Standards."  Results  of 
tests  are  not  certified  until  fees  are  paid. 

2.  SAMPLING 

The  following  should  be  noted  in  regard  to  submitting  samples 
for  test : 

Whenever  possible,  10  sheets  of  each  sample,  accurately  cut  12 
by  10  inches,  should  be  submitted.  These  sheets  should  be  picked 
out  in  such  a  manner  as  will  most  nearly  represent  an  average  of 
the  total  amount  in  question.  The  10  sheets  of  each  sample  should 
be  carefully  fastened  together,  and  one  outside  sheet  should  be 
marked  as  indicated  above. 

In  order  to  secure  representative  samples  for  test,  it  is  advisable 
to  proceed  as  follows : 

Case  lots. — Select  one  case  from  each  one-third  of  the  paper  in 
question,  and  then  select  one  sheet  from  each  one-third  of  each 
case.  The  tenth  sheet  should  be  taken  from  a  fourth  case.  After 
cutting  to  the  proper  size  for  forwarding  for  test,  the  remainder 
of  the  sample  should  be  saved  for  record  purposes.  Paper  in 
"frames  "  and  bundles  should  be  sampled  in  the  same  way.  In  the 
case  of  small  boxes  or  packages,  when  possible,  a  sheet  should  be 
obtained  from  each  of  10  boxes. 

Rolls. — Sample  by  taking  i  sample  from  each  of  10  rolls  not  less 
than  4  sheets  in  from  the  outside  of  the  roll. 

WASHINGTON,  September  18,  1920. 


sn 

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